Vaccines for the 21st Century A Tool for Decisionmaking (2000) / Chapter Skim
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Review of the Analytical Model
Review of the Analytical Model
Pages 93-108
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From page 93... ...
The committee examined 26 candidate vaccines, but included two distinct and alternative target populations for one candidate, thus 27 separate cases. As explained previously, the conditions selected for analysis are a mix of infectious diseases, cancers, and autoimmune disorders of health significance in the United States, and are conditions for which the committee judged that an adequate science base for vaccine development existed.
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From page 94... ...
/ Q , (1) where CEv is the cost-effectiveness ratio for case V, which is the analysis for a specific combination of health condition or pathogen, vaccine type, and target population; CD is the cost of vaccine development; C~ is the annual cost of immunizing the target population; Cc is the annualized costs of care averted by use of the vaccine; and Q is the annualized health benefit from use of the vaccine.
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From page 95... ...
Using the basic template, a separate file was created for each case. The following data were entered: age-specific incidence and death rates, average age at immunization, morbidity scenarios and associated quality-adjustment weights, typical health care provided for the condition and its associated costs, size of the target population, number of vaccine doses required, cost per dose, estimated vaccine efficacy, anticipated steady-state vaccine utilization rates among the target population, remaining development costs, expected time until licensure, and time from licensure until anticipated utilization rates are reached.
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From page 96... ...
to develop provisional estimates of age-specific health status at the population level. Final estimates for the NPHS will be based on the scoring system under development for the HUI Mark III, a revised HUI with eight component attributes (Torrance et al., 1992; Boyle et al., 1995~.
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From page 97... ...
Develop Morbidity Scenarios For each condition studied, the committee, with the advice of outside experts, developed morbidity scenarios to describe the characteristic sequences of acute or chronic health states, the duration of each health state, and the proportion of persons with the condition who experience each scenario. The scenarios also capture the premature mortality associated with a condition but which is delayed 1 or more years beyond the onset of the condition.
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From page 98... ...
To measure the impact of mortality and lifetime impairment, standard life table values were "quality adjusted" for the average health status of the population and discounted to their present value. Described here are the population-level quality adjustments used in the committee's analysis and the calculation of the discounted quality-adjusted life table values.
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From page 99... ...
For example, the discounting period for person-years lived in the age interval 60 65 with disease onset at age 20 was 42.5 years (62.5 - 20 = 42.5~. Once the discounted person-year values were obtained, standard life table calculations were used to calculate discounted quality-adjusted life expectancies at the selected ages of onset, with life expectancy at age x designated as eX .
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From page 100... ...
; combined values calculated as weighted average of male and female values (weights from distribution of U.S. population)
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From page 101... ...
Calculate Condition-Related Life Expectancies The discounted quality-adjusted life expectancies for selected ages were used to calculate the life expectancy in the population at the average age at onset
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From page 102... ...
in the age group 15-24. Adjust for the Underlying Health Status of the Population HUI Mark II-based quality-adjustment weights for health states were calculated from attribute scores assigned by the committee without reference to the underlying health status of the general population.
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From page 103... ...
The death rates obtained for each condition reflect deaths that occur within a short time following onset of the condition. The discounted quality-adjusted life expectancy at the average age at death fed ~ provides the estimate of QALYs lost due to deaths, which must be discounted for the period To + To, where To is the time from average age at vaccination to average age at onset and To is the difference between average age at onset of illness and average age at illness-related death.
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From page 104... ...
The age at death is calculated as the average age at onset of the condition plus the duration of health states experienced between onset and death. The discounted quality-adjusted life expectancy at the age at death is used to calculate the QALYs lost due to these deaths.
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From page 105... ...
, the number of doses required was altered to match the available evidence. The committee defined a target population for each vaccine considered, and the size of that target population was determined by using current estimates of the U.S.
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From page 106... ...
The cost cc was then discounted to adjust for To' the time from average age at vaccination to average age at onset of the condition, plus to' the duration of intervening health states that persist for at least 1 year. For continuing care required for a specified multiyear period rather than a period of days or weeks, it was necessary to allow for discounting of the stream of future costs.
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From page 107... ...
As was done for health benefits, calculations for separate subpopulations were summed to produce an estimate of total costs. VACCINE EFFICACY AND UTILIZATION The analysis includes adjustments for incomplete efficacy and use of the candidate vaccines, either of which will reduce the expected health benefits and savings in the cost of care.
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From page 108... ...
The first ratio examines the potential impact of the vaccine on morbidity and costs under the assumption that the vaccines are available immediately without any additional cost or time for development and that they are fully efficacious and are used by the entire target population. This comparison focuses attention on what might be considered an ideal vaccine benefit.
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